New light-developable photographic material and recording process



United States Patent 3,502,471 NEW LIGHT-DEVELOPABLE PHOTOGRAPHICMATERIAL AND RECORDING PROCESS Paul Desire Van Pee, Edegem, and JozefFrans Willems, Wilrijk-Antwerp, Belgium, assignors to Gevaert-Agfa N.V.,Mortsel-Belgium, a Belgian company No Drawing. Filed Oct. 11, 1966, Ser.No. 585,731 Claims priority, application Great Britain, Oct. 11, 1965,42,969/ 65 Int. Cl. G03c /32 US. Cl. 9645.2 .22 Claims ABSTRACT OF THEDISCLOSURE Photographic elements are defined which comprise aradiation-sensitive silver halide emulsion layer of the lightdevelopable type. The layer is applied from a coating compositioncontaining a silver iodide sol and/or a compound which will release freeiodide ions and a halogen acceptor corresponding to the formula or to atautomeric structure thereof as follows:

wherein each of R R R R and R is hydrogen, an alkyl group or an arylgroup, with the proviso, however, that at least one of the substituentsR and R is hydrogen; R, and R may also be the atoms necessary tocomplete a carbocylic ring. These light-developable silver halidematerials are useful in high-speed recording such as high-speedoscillographic recording of events which occur in rapid sequence, andthe like.

' The present invention relates to photographic elements comprising animproved light-developable radiation-sensitive silver halide emulsionlayer, as well as to a process for making records employing saidelements.

The light-developable silver halide materials have become of increasinginterest, for they possess desirable properties for high speedrecording, such as high speed oscillographic recording of events, whichoccur in rapid sequence, and the like.

Light-developable silver halide materials for direct recording areradiation-sensitive materials in which a visible image can be obtained,after an exposure to a high intensity source of radiation has beeninitially utilised to form a latent image, by an additional exposure toa radiation of lower intensity such as ditfuse daylight or artificiallight. The secondary exposure, also called latensification, is anoverall exposure, including exposing the areas in which the initiallatent image was formed as well as the surrounding background to anadditional amount of radiation.

It is known that in general, intense exposure favours the formation of alatent image in the interior of the grains while low-intensity exposureforms almost exclusively a surface latent image. The surface latentimage is the one developed by a usual chemical development whereas theinternal latent image is practically not developed by such processing.The light absorbed by the silver halide in the secondary exposureprovides the energy for the development of the internal latent image toa visible form (cf. H. Hunt High Speed Direct Recording Papers, Phot.Sci. Eng, vol. 5, No. 2, 1961).

3 ,5 02,47 1 Patented Mar. 24, 1970 wherein each of R R R R and Rrepresents a hydrogen atom, an alkyl group including a substituted alkylgroup or an aryl group including a substituted aryl group, with theproviso, however, that at least one of the substituents R and Rrepresents a hydrogen atom; R and R may also represent the atomsnecessary to complete a carbocyclic ring including a substitutedcarbocyclic ring, to light-developable radiation-sensitive silver halideemulsions results unexpectedly and surprisingly in the production of alight-developable material in which an improved image can be obtained,showing a favourable contrast between the image and the background (i.e.having a good net density) and having a very good stability as well as agood chemical developability. As will be seen from the exampleshereinafter, the effect of the simultaneous addition of the abovecompounds is much more important than the effects obtained on the onehand by the addition of the halogen acceptor alone and on the other handby the addition of the silver iodide sol and/ or the compound splittingoff iodide ions alone. When only a member of one of these two groups ofcompounds is incorporated into the light-developable radiation-sensitiveemulsion layer the difierence between the maximum and minimum density isconsiderably lower than when both groups are present together. Thisadditive effect is the more surprising since it was found that thiseffect could not be obtained in the case of a combination of a compoundsetting free iodide ions with many other generally known and often usedhalogen-acceptors e.g. hydrazothiocarbonamide, thiosemicarbazide andthiourea.

The improved light developable radiation sensitive photographic silverhalide elements according to the pres ent invention permit a rapidaccess to and prolonged examination of the image formed onphotodevelopment and also permit a chemical development and fixingtreatment in order to obtain permanent records of the traces or images.The material according to the present invention shows a high degree ofsensitivity to the trace beam coupled with a highly stable backgroundi.e. a background which is not very sensitive to low intensityradiation, thus resulting in a maximum contrast between the image andbackground. Thus, the images or traces obtained on lightdevelopment withelements according to the present invention are characterized by a highnet density, i.e. an optimum contrast between the image and background,a good resistance to fogging of the non-image areas even when exposedfor a long time to ambient lighting and even when no chemicaldevelopment occurs. Of course, when the traces or images produced onlatensification are exposed to ambient lighting for a long time the background darkens slowly, however, the contrast between image andbackground will remain for many hours. The

mages'or traces will not remain visible when permanently Compound 4:xposed to light. To keep a permanent record of the races or images, thematerial has to be chemically develped and fixed, preferably not toolong after the light- CHz-CH: N levelopment. Without said developmentand fixing step, he record will remain permanently only when thelightleveloped images are exposed to light infrequently and CHT'O :eptin the dark when not in use. Indeed, the image will :0 0:8 astpractically indefinite if protected from prolonged exlosure to stronglight. 6

Another advantage offered by the hght'developable4-methyl-3-thio-1,2,4-triazfospiro[5,5]undecane-35-dione :lements of theinvention is that it is possible to carry out a he light-developmentwhile supplying heat, whereby the Melnng o 210 Tjhls compound F be Pecorded image becomes almost immediately visible for pared accofdlng toPfoparatlon as descl'lbed further he reason that, when heating, it ispossible to increase the hereinafteright-intensity of the secondaryexposure without produe- ComP 5 ng fog. A probable explanation of thisphenomenon has 0,11, een given by Jacobs, Phot. Sci. & Eng, vol. 5, No.1, 1 .961. By the fact that when operating at elevated tem- )erature amore rapid image access is obtained, it is not i lecessary in thoseinstances Where there is recorded at 0:0 0:8 righ writing speeds andthus at high paper transport peeds, to expose considerable meters ofpaper to ambient I ight at the Same time, which would lead to a handlingCH3 roblem. Some oscillographs operate according to this -p y 'et xy3 tio-1,6-dihydro'as-triazinerrinciple: after the high-intensity exposurethe print-out material is passed over a heated plate while being ex-Melnng P This compound can be P :osed to fluorescent U.V. lamps so thata visible image pared according to Preparation as described further sproduced almost immediately. e te The following is a non-restrictivelist of halogen ac- Compound 6 eptors, which have proved to beparticularly suitable For use according to the present invention, andwhich (IJHHH :orrespond to the above general formula: N

Compound 1 nio NH E l 0:1 o=s HzC N NH H3C C T 1-phenyl-3-thio-1,6-dihydro-as-tri azine-3, 5 (2H,1H) -dione Melting point: 172-173 C.Preparation described by f Busch and Meussdorfier, Ber. 40, 1021 (1907)..H Compound 7 6,6-dimethyl-3-thio 1,fi-dihydro as-trrazine-lpfi 2H,4H)-dione Melting point: 248249 C. Preparation described by cm Fusco andRossi, Gazz. Chim. Ital. 89, 373 1954 1,

Compound 2 1 =S CH CH N 2- H2C\ O NH 02H CHz-Cg1-methyl-4ethyI-3-thio-1,'6-dihydro=as-trlazine- O=O\ /C=S3,5(2H,4H)-dione N Melting point: 129 C. This compound can be prepared kaccording to Preparation 4 as described further herein-3-thio-1,2,4-triazaspiro['5,5]undecane-3,5-dione after' PREPARATION 1Melting 224 Preparation descnbed by Fusco A. Preparation of theintermediate product 1-(1'-cyano- 1nd ROSSI, GaZz. Chlm- Ital. 89, r ey1 y 4 et y th s m ca ba de Compound 3 21 g. of 4-methylthiosemicarbazide are dissolved in H 80 ccs. of a mixture of ethanol andwater (1:1). Whilst H30 5 stirring the solution, there are successivelyadded at room temperature: 11.5 ccs. of acetic acid, a solution of 13 g.Hie-C I of potassium cyanide in 25 ccs. of Water and 12.6 ccs. of 0:00:8 acetone. The reaction mixture is refluxed for 1 hour. After cooling,the crystals formed are filtered by suction (yield: 34.5 g.meltingpoint: 197-203 C.) and recrys- CH3 tallized from 1600 ccs. of ethanol.4,6,(i-trimethyl-S-thio-l,G-dihydro-as-triazine- Yield: 25.5 g.1-(1'-cyano-1'-methyl-ethyl)-4-methylthio-semicarbazide. Melting point:210 C. Melting point: 190 C. This compound can be preMicroanalysis.-Calculated for C H N S, molecular pared according toPreparation 1 as described further weight: 172 (percent): C, 41.90; H,7.03; S, 18.64. lereinafter. Found (percent): C, 42.45; H, 6.87; S.18.39.

B. Preparation of Compound 3 800 g. of the obtained 1-(1-cyano-1'-methyl-ethyl)-4- methyl-thiosemicarbazide are dissolved in 3300 ccs. ofan aqueous hydrochloric acid solution (d.: 1.17) and heated for 24 h. at80 C. On cooling, ammonium chloride crystallizes and is filtered bysuction. The filtrate is brought at pH 3-4 by means of 2200 ccs.ammonium hydroxide, whereby4,6,6-trimethyl-3-thio-1,6-dihydro-astriazine-3,5 (2H, 4H)-di0neprecipitates together with ammonium chloride. The precipiate iscrystallized from water (5500 ccs.).

Yield: 160 g. of 4,6,6-trimethyl-3-thio-1,6-dihydro-astriazine-3,5 (2H,4H)-dione. Melting point: 190 C.

Microanalysis.-Calculated for C H ON S, molecular weight: 173 (percent):C, 41.65; H, 6.41; S, 18.54. Found (percent): C, 41.92; H, 6.38; S,18.33.

PREPARATION 2 A. Preparation of the intermediate product1-(1'-cyanocyclohexyl) -4-methy1-thio semicarbazide 105 g. of4-methyl-thiosemicarbazide are dissolved in 400 ccs. of a mixture ofethanol and water (1 :1). Whilst stirring the solution at C. there aresuccessively added: 57.5 ccs. of acetic acid, a solution of 65 g. ofpotassium cyanide in 125 ccs. of water and 98 g. of cyclohexanone. Thereaction mixture is refluxed for 2 hours, whilst stirring. Aftercooling, the crystals formed are filtered by suction and washed withethanol and ether.

Yield: 189 g. 1-(1-cyano-cyclohexyl)-4-methyl-thiosemicarbazide. Meltingpoint: 200 C.

Microanalysis.Calculated for C H N S, molecular weight: 212 (percent):C, 50.99; H, 7.61; S, 15.13. Found (percent): C, 51.22; H, 7.84; S,15.00.

B. Preparation of Compound 4 189 g. ofl-(1'-cyano-cyclohexyl)-4-methyl-thiosemicarbazide are dissolved in 1375ccs. of an aqueous hydrochloric acid solution (d.=l.17) and heated for24 hours at 80 C. After cooling, the precipitate formed is filtered bysuction and washed with water, whereafter it is recrystallized from 3500ccs. of ethanol.

Yield: 125 g. of 4-methyl-3-thio-1,2,4-triazospiro[5,5]undecane-3,5-dione. Melting point: 210 C.

Microanalysis.Calculated for C H ON S, molecular weight 213 (percent):C, 50.75; H, 7.10; S, 15.05. Found (percent): C, 50.47; H, 7.08; S,15.05.

PREPARATION 3 70 g. of 1-phenyl-l-ethoxyacetyl-hydrazine hydrochlorideare dissolved in 450 ccs. of water. By adding 17.1 g. of ammoniumcarbonate 1 aq., the base is set free from its hydrochloride whereuponit is extracted with ether. After drying the etheric solution overmolecular sieves, a

solution of 15.6 g. of methylisothiocyanate in 220 ccs. of-

PREPARATION 4 45 g. of l-methyl-l-ethoxyacetyl hydrazine hydrochlorideare suspended in 230 ccs. anhydrous ether and whilst thoroughly stirringat 0 C. ammonia gas is introduced. The formed ammonium chloride isremoved by filtration. By evaporation of the ether of the filtrate, anoil is left which is again dissolved in 205 ccs. anhydrous ether andthis solution is added to a solution of 21.6 ccs. of ethylisothiocyanatein 205 ccs. of anhydrous ether. After stirring for half an hour at roomtemperature, the ether is evaporated. The residue is dissolved in ccs.of anhydrous ethanol and whilst stirring at 0 C., a solution of 16.2 g.of potassium hydroxide in ccs. of anhydrous ethanol is dropwise added.After stirring for one hour, the ethanol is evaporated. The remainingyellow oil is added to 200 ccs. of water and acidified with acetic acid.The precipitate is crystallized from 50 ccs. of ethanol.

Yield: 13 g. of 1-methyl-4-ethyl-3-thio-1,6-dihydro-astriazine-3,5(2H,4H)-dione. Melting point: 129 C.

Microanalysis.Calculated for C H ON S, molecular weight: 173 (percent):C, 41.65; H, 6.41; S, 18.54. Found (percent): C, 41.73; H, 6.29; S,18.60.

The amount of halogen acceptor according to the above general formulathat is incorporated into the silver halide emulsion layer according tothe present in- 'vention may vary within very wide limits viz from about0.01 g. to about 20 g. per mole of silver halide, but is preferablycomprised between about 0.1 g. and about 5 g. per mole of silver halide.

According to the invention, the halogen acceptor corresponding to theabove general formula may also be applied together with other halogenacceptors. Very good results have been obtained when using incombination with the halogen acceptors of the present invention thehalogen acceptors described in our co-pending applications entitledLight-Developable Photographic Material and Recording Process andImproved Light-Developable Photographic Material and Recording Process,both filed on even date herewith.

Suitable compounds setting free iodide ions are among others inorganicand organic iodides, organic compounds with labile iodine atom and oniumchloroiodates.

Suitable inorganic iodides are for instance the following water-solubleiodides: calcium iodide, ammonium iodide, lithium iodide, magnesiumiodide, potassium iodide and sodium iodide.

Suitable organic iodides are for instance the iodides having thefollowing structural formulae:

1-methyl-8-hydroxy-qui1roliniun1 iodide lCH3 1-methyl-2-iodo-quinoliniumiodide 1,2,3,4-tetrahydro-8-hydroxy-1,l-dimethyl-quinolinlum iodidebenzyltriphenylphosphonium iodide 3,5-dimorpholino-dithiolium dio'de COOCH3 [Cla- 31 3):

#crimethyl o-methoxycarbonyl-auilinium) dichloroio'datebenzyltriphenyl-phosphonium dichloroiodate Instead of or in addition toa compound setting free Iodide ions, a silver iodide sol comprising anappropriate protective colloid can be added with the same effect to :hesilver halide emulsion. A very suitable silver iodide sol can beprepared by slowly adding while strongly rtirring the following solutionA to the following solu- :ion B, both solutions being heated to 35 C.

Solution B:

3NKI.17 ccs. gelatin.40 g. water up to 1 litre Solution A:

3NAgNO .17 ccs. water up to 1 litre The amount of compound setting freeiodide ions may also vary within very wide limits. In general an amountrom about 0.01 g. to about 20 g. preferably from about ).1 g. to about 5g. per mole of silver halide is applied. lhe same applies to the limitswithin which the silver odide sol is used. In the latter case the aboveamounts -elate to the silver iodide and not to the total sol. Thelddition of a member selected from a. silver iodide sol and at least onecompound setting free iodide ions, and

preferably also the addition of the halogen-acceptor occurs after theemulsion preparation and preferably just before coating on a suitablesupport. Except the addition of the silver iodide sol, any otheraddition can occur from a solution of the compound involved in asuitable slvent, which is mostly water but may also be an organicsolvent.

By the addition to a silver halide emulsion of a compound setting freeiodide ions or of a silver iodide sol, silver iodide is produced on thesurface of the silver halid grains of the emulsion, in the former caseby conversion and in the latter by adsorption. The formation of silveriodide at the surface of the grains and the favourable effects resultingtherefrom for the method of the present invention can also be attainedby conducting the emulsion layer obtained after coating through asolution, preferably an aqueous solution of a compound setting freeiodide ions, or by treating this emulsion layer in some other waytherewith.

According to the invention any silver halide emulsion of thelight-developable type may be used. These kinds of emulsions are verywell known to those skilled in the art. They mainly or entirely form aninternal latent image and only to a little extent an external latentimage.

A silver halide emulsion that mainly or entirely forms an internallatent image and only to a little extent an external latent image is anemulsion in which only few or no exposed grains at all are developableinto silver by a developing solution that cannot act as a developer fora latent image inside the grains i.e. a so-called surface develop-er,such as:

p-Hydroxphenyl glycine-10 g. Sodium carbonate (cryst.)l00 g. Water to1000 ccs.

and wherein the exposed grains are well developable to silver by adeveloping solution that acts as a developer for latent image inside thegrains i.e. a so-called internal developer such as the followingsolution:

Hydroquinone15 g. Monomethyl-p-aminophenol sulphate-1.5 g. Sodiumsulphite (anhydrous)--50 g. Potassium bromide-10 g.

Sodium hydroxide25 g.

Sodium thiosulphate (cryst.)-20 g.

Water to 1000 ccs.

By a silver halide emulsion that mainly forms internal latent image andlittle external latent image there is more particularly meant a silverhalide emulsion, a test layer of which upon exposure to a lightintensity scale for a fixed time between A00 and 1 sec. and developmentfor 3 min. at 20 C. in the above internal developer, exhibits a maximumdensity at least 5 times the maximum density obtained when an identicaltest layer of the said silver halide emulsion is equally exposed andthen developed for 4 min. at 20 C. in the above surface developer.

Silver halide emulsions that meet the above requirement and hence aresuitable for being employed in the process of the invention aregenerally not or only slightly chemically ripened silver halideemulsions, since the extent of the surface latent image-formingcapability increases with the degree of chemical ripening.

Silver chlorobromide and silver bromide emulsions have proved to bespecially suitable for the purpose of the invention. When theseemulsions comprise minor amounts of silver iodide, preferably not morethan 5 mole percent relative to the total amount of silver halide, theyare just as Well suitable.

The silver halide emulsions for use in the present process are generallygelatin silver halide emulsions. However, the gelatin may wholly orpartially be replaced for instance by another protein, a hydrophilic notproteinaceous colloid or a synthetic polymeric substance applied from anaqueous dispersion. The light-sensitive silver halide emulsions may beprepared according to all known and conventional techniques for emulsionpreparation. A method according to which emulsions are prepared, andwhich has proved to be particularly suitable for the purpose of theinvention, is the so-called conversion method according to which anemulsion of a silver salt that has a higher degree of solubility thansilver bromide is converted into a silver chlorobromide or a silverbromide emulsion that occasionally contains small amounts of silveriodide. This conversion is carried out preferably very slowly forinstance by several consecutive steps.

The emulsions can, if desired, be modified prior to coating by theaddition of all kinds of ingredients, which are generally known in theart of emulsion preparation and some of which will be set outspecifically hereinafter.

Among the said ingredients may first be mentioned the common additives,for light-sensitive silver halide material such as hardening agents e.g.formaldehyde, coating aids, e.g. saponine, plasticizers, e.g. glycerol,optical sensitisers of the class of the cyanine dyes, the merocyaninedyes, etc., development accelerators, compounds that render the materialmore resistant to wrinkling and less brittle etc.

Furthermore specific ingredients may be incorporated also. Among thesemay be mentioned more particularly:

Thiocyanates, such as potassium thiocyanate, which further stabilise thelight-developed image;

Compounds or mixtures of compounds reducing the background density onlatensification e.g. lead salts, and prreferably cadmium salts; thesesalts are preferably salts that are water-soluble such as lead acetate,lead iodide, lead nitrate, cadmium iodide, cadmium chloride, cadmiumbromide, cadmium nitrate, etc.; they give rise to a decrease of theminimum density without, however, decreasing the maximum density to thesame extent so that as a result thereof the contrast is enhanced. Saidsalts may be added to the emulsion during the emulsion preparation orthe conversion of the silver salt emulsion by means of a bromide as wellas just before coating the emulsion on a support. They are added inamounts varying from about 1 g. to about 20 g., preferably from about 5g. to about g. per mole of silver halide.

The amount of gelatin applied in emulsion making is preferably such thatper kg. of emulsion ready for coating from about g. to about 150 g. ofgelatin is present.

The amount of silver nitrate used in emulsion making preferably variesfrom about 50 to about 200 g. per kg. of emulsion.

The emulsion is generally coated in such a way that 1 kg. of emulsioncovers approximately from about 20 to about 30 sq. m. of support.

Suitable support for the elements of this invention include the flexiblesupports used in the prior art for lightwriting and oscillographicrecording. They may be any type of paper, as well as films of cellulosenitrate, cellulose acetate, poly(vinyl acetal), polystyrene,po1y(ethylene terephthalate) and other synthetic resins. Supports ofglass, metal, and other substances are not excluded. In this connectionconventional photographic base papers may be conveniently utilised.

In order to form an image in the light-developable radiation-sensitivephotographic elements acccording to the present invention, said elementsare first exposed to a high-intensity actinic radiation e.g. from Xenontubes, U.V.-lamps or high-pressure mercury arc lamps as used in certainoscillographs.

The high-intensity radiation source used for the initial or firstexposure of the light-developable material is generally rich in blue andultraviolet radiation but said radiation may be any light or otherelectromagnetic radiation of either visible or invisible wave lengths,X-rays, gamma rays or an electron beam. After the initial exposure thematerial may be light-developed by exposure to low intensity daylight,incandescent light or fluorescent light, or by the use of photofloodlamps as commonly used in photography. This secondary exposure must notnecessarily be performed with the aid of an actinic radiation source.When light-developing with common oflice lighting or daylight the imagebecomes visible after 15- 30 seconds, attaining maximum density inseveral minutes. In certain instances i.e. for obtaining practicallyimmediately visible traces or images it may be advan: tageous, asalready stated above, to carry out the development while supplying heat.This can be carried out by running the material over a hot plate at -180C. in the secondary exposure step.

The sharpness of the recorded trace or image may be further increased bya short preliminary exposure of the light-developableradiation-sensitive material according to the invention to ordinarylight e.g. daylight, prior to exposing the material to thehigh-intensity radiation. Indeed, by this short preliminary exposure thegradation in the toe of the characteristic curve and the contrast or netdensity of the recorded trace or image are increased.

If desired the material may be chemically developed and fixed before,during or after the photo-development, latensification, or secondaryexposure. This development is of the internal type which means that ittakes place in the presence of an energetic silver halide solubilisingagent, e.g. sodium thiosulphate,,which is mostly present in thedeveloper itself. Said chemical development advantageously occurs in thepresence of an anti-fogging agent. The halogen acceptor used canfunction as such at least when it possesses good antifogging properties.The antifogging agent may be incorporated in at least one of thecomposing layers of the photographic element used and/ or in thedeveloper. Examples of suitable anti-fogging agents areZ-mercapto-ethyl-carbanilate, l-phenyl-Z-tetrazoline-S-thione and 4,5,6, 7-tetrabromo- 1 H-benzotriazole.

It was noticed that the advantage of the chemical development oflight-developable silver halide material in the presence of anti-foggingagents does not only apply to the material according to the presentinvention but also to any photographic material of the light-developabletype.

EXAMPLE 1 A light-sensitive photographic silver bromide emulsion of thelight-developable type, i.e. that mainly forms an internal latent imageand only to a little extent an external latent image is prepared byconversion of a silver chloride emulsion into a silver bromide emulsion.Said silver bromide emulsion is prepared so that an amount of silverbromide equivalent to g. (0.7 mole) of silver nitrate is present per kg.of emulsion. The usual emulsion ingredients and coating aids areincorporated into the emulsion, and in addition thereto anorthochromatic sensitizing agent, and 8 g. of cadmium bromide per kg. ofemulsion for reducing the background density.

The emulsion obtained is divided into many different emulsion samples.To these samples are added the additives accoring to the invention aslisted in the table hereinafter. The halogen-acceptor is added in anamount of 40 ccs. of a 1% by weight solution in a suitable solvent perkg. of emulsion whereas the compound setting free iodide ions, in thisparticular case potassium iodide, is added in an amount of 10 ccs. of a4% by weight aqueous solution per kg. of emulsion.

All emulsion samples obtained are coated on conventional photographicpaper supports such that an amount of silver halide equivalent to 4 g.of silver nitrate is present per sq. m. of light-sensitive material.

All light-sensitive materials obtained are subjected to the followingidentical successive treatments:

1) They are exposed in a flash-sensitometer Mark VI of Edgerton,Germeshausen and Grier for 10' sec. through a step wedge with a constantof 0.3.

TABLE Number Material Additive AD of steps 1 None 12 6 KI alone 0 32 6Compound 1 alone 0 28 6 4 Compound 1+KI 0 39 7 5 Compound 2 alone 0. 267 6 Compound 2+KI 0.86 7

As can be seen from the results listed in the above table the materialscomprising potassium iodide or halogenacceptor alone show lessdifference between the image and background densities than the materialscomprising both potassium iodide and halogen-acceptor; thus the contrastbetween image and non-image areas is enhanced.

EXAMPLE 2 A light-sensitive photographic silver bromide emulsion of thelight-developable type is prepared as described in Example 1. Theemulsion obtained is now divided into 3 samples A, B and C. To emulsionsamples B and C is added per kg. of emulsion as anti-fogging agent 5ccs. and ccs. respectively of a 5% by weight solution in ethanol of1-phenyl-2-tetrazoline-5-thione. To sample A no antifogging agent isadded.

Before coating in the way as described in Example 1 each emulsion sampleon a conventional photographic paper support 10 ccs. of a 2.5% by weightsolution of 6,6 dimethyl-3-thio-1,6-dihydro-as-triazine-3,5-(2H,4H)-dione in ethylene glycol monomethyl ether and 10 ccs. of a 4% by weightaqueous solution of potassium iodide are added per kg. of emulsion.

Each of the 3 materials obtained is exposed to high intensity-radiationas described in Example 1, and photodeveloped by exposure for min. toordinary office fluorescent light with a total light intensity of 240Lux.

Immediately thereafter the samples are developed at 20 C. for 1 /2 min.in an internal developer with the following composition:

Hydroquinone-6 g. Monomethyl-p-aminophenol sulphate-3 g. Sodium sulphite(anhydrous)30 g. Potassium bromide-2.5 g.

Sodium carbonate (anhydrous)50 g. Sodium thiophosphate (cryst.)-1O g.Water to 1000 ccs.

The samples are then fixed, rinsed and dried in the usual way.

After development the image densities and background densities of eachof the materials are determined and listed in the following table.

TABLE Maximum Minimum Sample density density AD A 1. 23 1. 16 0. ()3B 1. 20 0. 98 0. 27 C 0. 63 0. 30 0. 32

12 EXAMPLE 3 4 light-sensitive photographic silver bromide materials ofthe light-developable type are prepared as described in Example 1,however, without cadmium bromide and with additives according to theinvention as listed in the table hereinafter. The mentionedconcentrations of these additives are per kg. of emulsion ready forbeing coated.

All light-sensitive materials thus obtained are exposed andphoto-developed for 15 min. as described in Example 1. The maximum andminimum densities are measured in a MacBeth reflection densitometer. TheAD values too have been listed.

Max. Min. Material Additive dens. dens. AD

1 0. 42 0. 26 0. 16 2 12.5 cos. of a solution of 1 g. 0.69 0.39 0.30

of compound 1 in 100 ccs. of ethylene glycol monomethyl ether. 3 100 g.of silver iodide sol 0. 0. 48 0.37

prepared as described herein. 4 Both said additives of the 0. 82 0. 400. 42

materials 2 and 3 together.

As can be seen from the above results, the materials mto WhlChhalogen-acceptor or silver iodlde sol alone has been incorporated showless difference between the image and background densities than thematerials to which both halogen acceptor and silver iodide sol have beenadded. Thus, the contrast between image and nonimage areas has beenenhanced.

We claim:

1. Photographic element comprising a radiationsensitive silver halideemulsion layer of the lightdevelopable type, applied from a coatingcomposition, to which are added (1) at least one member selected from asilver iodide sol and a compound setting free iodide ions, and

(2) at least one halogen acceptor corresponding to the following generalformula or to a tautomeric structure thereof:

wherein each of R R R R and R is hydrogen, an alkyl group or an arylgroup, with the proviso, however, that at least one of the substituentsR and R is hydrogen; R and R may also be the atoms necessary to completea carbocyclic ring.

2. Photographic element according to claim 1, wherein said compoundsetting free iodide ions is an organic or a water-soluble inorganiciodide.

3. Photographic element according to claim 2, wherein said water-solubleinorganic iodide is potassium iodide.

4. Photographic element according to claim 1, wherein the silver iodideof the sol and/or the compound setting free iodide ions is (are) presentin an amount of from 0.1 to 5 g. per mole of silver halide. 9

5. Photographic element according to claim 1, wherein thehalogen-acceptor corresponding to the general formula:

t. wherein each of R R R R and R is hydrogen, an alkyl group or an arylgroup, with the proviso, however,

13 that at least one of the substituents R and R is hydrogen; R and Rmay also be the atoms necessary to complete a carbocyclic ring, ispresent in an amount of from 0.1 to 5 g. per mole of silver halide.

6. Photographic element according to claim 1, wherein said emulsionlayer is essentially a silver bromide emulsion layer.

7. Photographic element according to claim 1, wherein said emulsionlayer also comprises a cadmium and/or a lead salt.

8. Photographic element according to claim 7, wherein said salt is addedin an amount comprised between 5 g. and g. per mole of silver halide.

9. Photographic element according to claim 1, wherein said emulsionlayer also comprises a thiocyanate.

10. Photographic element according to claim 9, wherein said thiocyanateis potassium thiocyanate.

11. Photographic element according to claim 1, wherein said emulsionlayer also comprises an anti-fogging agent.

12. Photographic element according to claim 11, wherein saidanti-fogging agent is 1-phenyl-2-tetrazoline-5- thione.

13. Photographic element according to claim 1, wherein said emulsionlayer also comprises an optical sensitising agent.

14. Photographic element according to claim 1,.wherein the memberselected from a silver iodide sol and a compound setting free iodideions is added to the radiationsensitive coating composition just beforecoating.

15. Photographic element according to claim 1, wherein thehalogen-acceptor corresponding to the general formula:

wherein each of R R R R and R is hydrogen, an alkyl group or an arylgroup, with the proviso, however, that at least one of the substituentsR and R is hydrogen; R and R may also be the atoms necessary to completea carbocyclic ring, is added to the radiation-sensitive coatingcomposition just before coating.

16. Photographic element comprising a radiationsensitive silver halideemulsion layer of the lightdevelopable type, the silver halide grains ofwhich contain silver iodide at their surface, wherein said emulsionlayer contains at least one halogen-acceptor corresponding to thefollowing general formula or to a tautomeric structure thereof:

wherein each of R R R R and R is hydrogen, an alkyl group or an arylgroup, with the proviso, however, that at least one of the substituentsR and R is hydrogen; R and R may also be the atoms necessary to completea carbocyclic ring.

17. Process for recording traces or images comprising exposing to a highintensity actinic radiation a photographic element according to claim 1,and light-developing the latent image formed by said initial exposure byoverall exposing said element to a radiation of lower intensity.

18. Process according to claim 17, wherein an internal development stepand a fixing step are included before, during or shortly after saidlight-development.

19. Process according to claim 18, wherein the development step takesplace in the presence of an anti-fogging agent.

20. Process according to claim 19, wherein said antifogging agent is1-phenyl-2-tetrazoline-5-thione.

21. Process according to claim 17, wherein said lightdevelopment iscarried out while applying heat.

22. Process according to claim 21, wherein said heat is supplied byrunning the element over a hot plate heated at -180 C.

References Cited UNITED STATES PATENTS 3,260,605 7/1966 Sutherns 961073,287,137 11/1966 McBride 96107 3,367,780 2/1968 Fix et al. 96-l02NORMAN G. TORCHIN, Primary Examiner ALFONSO T. SURO PICO, AssistantExaminer US. Cl. X.R. 9666.5, 107

